The present invention relates to a carbonylation catalyst, and specifically, to a vapor-phase carbonylation catalyst having platinum and tin associated with a solid support material. More particularly, the present invention relates to a vapor-phase carbonylation catalyst having a solid-phase component which includes platinum and tin associated with a solid support material and at least one vaporous halide promoter component. The carbonylation catalyst is particularly useful for the production of acetic acid, methyl acetate and mixtures thereof from methanol, dimethyl ether and methyl ester and ester-alcohol mixtures.
Lower carboxylic acids and esters such as acetic acid and methyl acetate have been known as industrial chemicals for many years. Acetic acid is used in the manufacture of a variety of intermediary and end-products. For example, an important derivative is vinyl acetate which can be used as monomer or co-monomer for a variety of polymers. Acetic acid itself is used as a solvent in the production of terephthalic acid, which is widely used in the container industry, and particularly in the formation of PET beverage containers.
There has been considerable research activity in the use of metal catalysts for the carbonylation of lower alkyl alcohols, such as methanol, and ethers to their corresponding carboxylic acids and esters, as illustrated in equations 1-3 below:ROH+CO→RCOOH  (1)2ROH+CO→RCOOR+water  (2)ROR′+CO→RCOOR  (3)
Carbonylation of methanol is a well known reaction and is typically carried out in the liquid phase with a catalyst. A thorough review of these commercial processes and other approaches to accomplishing the formation of acetyl from a single carbon source is described by Howard et al. in Catalysis Today, 18, 325-354 (1993). Generally, the liquid phase carbonylation reactions for the preparation of acetic acid using methanol are performed using homogeneous catalyst systems comprising a Group VIII metal and a halogen component such as iodine or bromine or an iodine or bromine-containing compound such as hydrogen iodide, hydrogen bromide, methyl iodide, or methyl bromide. Rhodium is the most common Group VIII metal catalyst and methyl iodide is the most common promoter. These reactions are conducted in the presence of water to prevent precipitation of the catalyst.
These recently developed processes represent a distinct improvement over the classic carbonylation processes wherein such feed materials have been previously carbonylated in the presence of such catalyst systems as phosphoric acid, phosphates, activated carbon, heavy metal salts and metal carbonyls such as cobalt carbonyl, iron carbonyl and nickel carbonyl. All of these previously known processes require the use of extremely high partial pressures of carbon monoxide. They also have the disadvantage of requiring higher catalyst concentrations, longer reaction times, and higher temperatures to obtain substantial reaction and conversion rates. This results in needing larger and more costly processing equipment and higher manufacturing costs.
A disadvantage of a homogeneous phase carbonylation process is that additional steps are necessary for separating the products from the catalyst solutions, and there are always handling losses of the catalyst. Losses of the metal in the catalyst can be attributed to several factors, such as the plating-out of the active metal onto piping and process equipment thereby rendering the metal inactive for carbonylation purposes and losses due to incomplete separation of the catalyst from the products. These losses of the metal component are costly because the metals themselves are very expensive.
Schultz, in U.S. Pat. No. 3,689,533, discloses using a supported rhodium catalyst for the carbonylation of alcohols to form carboxylic acids in a vapor-phase reaction. Schultz further discloses the presence of a halide promoter.
Schultz in U.S. Pat. No. 3,717,670 describes a similar supported rhodium catalyst in combination with promoters selected from Groups IB, IIIB, IVB, VB, VIB, VIII, lanthanide and actinide elements of the Periodic Table.
Uhm, in U.S. Pat. No. 5,488,143, describes the use of alkali, alkaline earth or transition metals as promoters for supported rhodium for the halide-promoted, vapor phase methanol carbonylation reaction. Pimblett, in U.S. Pat. No. 5,258,549, teaches that the combination of rhodium and nickel on a carbon support is more active than either metal by itself.
In addition to the use of iridium as a homogeneous alcohol carbonylation catalyst, Paulik et al., in U.S. Pat. No. 3,772,380, describe the use of iridium on an inert support as a catalyst in the vapor phase, halogen-promoted, heterogeneous alcohol carbonylation process.
European Patent Application EP 0 759 419 A1 pertains to a process for the carbonylation of an alcohol and/or a reactive derivative thereof. EP 0 759 419 A1 discloses a carbonylation process comprising a first carbonylation reactor wherein an alcohol is carbonylated in the liquid phase in the presence of a homogeneous catalyst system and the off gas from this first reactor is then mixed with additional alcohol and fed to a second reactor containing a supported catalyst. The homogeneous catalyst system utilized in the first reactor comprises a halogen component and a Group VIII metal selected from rhodium and iridium. When the Group VIII metal is iridium, the homogeneous catalyst system also may contain an optional co-promoter selected from the group consisting of ruthenium, osmium, rhenium, cadmium, mercury, zinc, indium and gallium. The supported catalyst employed in the second reactor comprises a Group VIII metal selected from the group consisting of iridium, rhodium, and nickel, and an optional metal promoter on a carbon support. The optional metal promoter may be iron, nickel, lithium and cobalt. The conditions within the second carbonylation reactor zone are such that mixed vapor and liquid phases are present in the second reactor. The presence of a liquid phase component in the second reactor inevitably leads to leaching of the active metals from the supported catalyst which, in turn, results in a substantial decrease in the activity of the catalyst and costly replacement of the active catalyst component.
The literature contains several reports of the use of rhodium-containing zeolites as vapor phase alcohol carbonylation catalysts at one bar pressure in the presence of halide promoters. The lead references on this type of catalyst are presented by Maneck et al. in Catalysis Today, 3, 421-429 (1988). Gelin et al., in Pure & Appl. Chem., Vol. 60, No. 8, 1315-1320 (1988), provide examples of the use of rhodium or iridium contained in zeolite as catalysts for the vapor phase carbonylation of methanol in the presence of halide promoter. Krzywicki et al., in Journal of Molecular Catalysis, 6, 431-440 (1979), describe the use of silica, alumina, silica-alumina and titanium dioxide as supports for rhodium in the halide-promoted vapor phase carbonylation of methanol, but these supports are generally not as efficient as carbon. Luft et al., in U.S. Pat. No. 4,776,987 and in related disclosures, describe the use of chelating ligands chemically attached to various supports as a means to attach Group VIII metals to a heterogeneous catalyst for the halide-promoted vapor phase carbonylation of ethers or esters to carboxylic anhydrides.
Evans et al., in U.S. Pat. No. 5,185,462, describe heterogeneous catalysts for halide-promoted vapor phase methanol carbonylation based on noble metals attached to nitrogen or phosphorus ligands attached to an oxide support.
Panster et al., in U.S. Pat. No. 4,845,163, describe the use of rhodium-containing organopolysiloxane-ammonium compounds as heterogeneous catalysts for the halide-promoted liquid phase carbonylation of alcohols.
Drago et al., in U.S. Pat. No. 4,417,077, describe the use of anion exchange resins bonded to anionic forms of a single transition metal as catalysts for a number of carbonylation reactions including the halide-promoted carbonylation of methanol. Although supported ligands and anion exchange resins may be of some use for immobilizing metals in liquid phase carbonylation reactions, in general, the use of supported ligands and anion exchange resins offer no advantage in the vapor phase carbonylation of alcohols compared to the use of the carbon as a support for the active metal component. Moreover, these catalysts are typically unstable at elevated temperatures making them poorly suited to a vapor phase process.
Nickel on activated carbon has been studied as a heterogeneous catalyst for the halide-promoted vapor phase carbonylation of methanol. Relevant references to the nickel-on-carbon catalyst systems are provided by Fujimoto et al. in Chemistry Letters 895-898, (1987). Moreover, Fujimoto et al. in Journal of Catalysis, 133, 370-382 (1992) observed increased rates when hydrogen is added to the feed mixture. Liu et al., in Ind. Eng. Chem. Res., 33 488-492, (1994), report that tin enhances the activity of the nickel-on-carbon catalyst. Mueller et al., in U.S. Pat. No. 4,918,218, disclose the addition of palladium and optionally copper to supported nickel catalysts for the halide-promoted carbonylation of methanol. In general the rates of reaction provided by nickel-based catalysts are lower than those provided by the analogous rhodium-based catalysts when operated under similar conditions.
Other single metals supported on carbon have been reported by Fujimoto et al. in Catalysis Letters, 2, 145-148 (1989) to have limited activity in the halide-promoted vapor phase carbonylation of methanol. The most active of these metals is Sn. Following Sn in order of decreasing activity are Pb, Mn, Mo, Cu, Cd, Cr, Re, V, Se, W, Ge and Ga. None of these other single metal catalysts are nearly as active as those based on Rh, Ir, Ni or the catalyst of the present invention.
Yagita and Fujimoto in Journal of Molecular Catalysis, 69, 191-197 (1991) examined the role of activated carbon in a metal supported catalyst and observed that the carbonylation activities of Group VIII metals supported on activated carbon are ordered by the affinities between the metal and the halogen.
Feitler, in U.S. Pat. No. 4,612,387, describes the use of certain zeolites containing no transition metals as catalysts for the halide-free carbonylation of alcohols and other compounds in the vapor phase.
U.S. Pat. No. 5,218,140, describes a vapor phase process for converting alcohols and ethers to carboxylic acids and esters by the carbonylation of alcohols and ethers with carbon monoxide in the presence of a metal ion exchanged heteropoly acid supported on an inert support. The catalyst used in the reaction includes a polyoxometallate anion in which the metal is at least one of a Group V(a) and VI(a) is complexed with at least one Group VIII cation such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd or Pt as catalysts for the halide-free carbonylation of alcohols and other compounds in the vapor phase.
In accordance with the present invention, a platinum and tin solid supported catalyst is provided for heterogeneous vapor-phase carbonylation of reactants comprising lower alkyl alcohols, ether and ester derivatives of the alcohols, and mixtures of ester-alcohols for producing esters and carboxylic acids. Surprisingly, the platinum and tin catalyst demonstrate significant rate improvements when compared to catalysts containing platinum as the sole active metal.